Asphaltenes are high molecular weight hydrocarbons having a chemical structure that can include stacked sheets of fused aromatic rings. Due to their high molecular weight (e.g., greater than about 1,000 daltons) asphaltenes are found within the least volatile fraction after distillation of crude oil. Asphaltenes also can be found in oil sands along with minerals and other hydrocarbons.
High molecular weight hydrocarbons, such as asphaltenes, typically are not suitable for use as fuel oil (e.g., as a replacement for diesel fuel used in the transportation industry), as a solvent to reduce the viscosity of other fluids so that they can be transported through a pipeline, or as feedstock for the production of petroleum-derived organic chemicals. Conventionally, the high molecular weight hydrocarbons produced during refinement processes are either discarded or broken down into lower molecular weight hydrocarbons using a process generally known as “cracking.” For example, hydrogen can be added (e.g., by subjecting the high molecular weight hydrocarbons to a hydrotreating process) or carbon can be subtracted (e.g., by subjecting the high molecular weight hydrocarbons to a coking process). Hydrotreating typically includes reacting the high molecular weight hydrocarbons at high pressures in the presence of catalysts. Coking typically includes breaking down the high molecular weight hydrocarbons into two or more fractions, such as a light paraffinic or aromatic liquid fraction and a heavy solid coke fraction.
Conventional cracking processes can be used to derive value from high molecular weight hydrocarbons, but they typically are expensive due to high energy demands and the cost of capital equipment and catalysts. With regard to the heaviest fraction, which requires the most processing, conventional cracking processes often prove to be uneconomical. In addition, conventional cracking processes typically are ineffective at breaking down large asphaltene molecules and often result in the precipitation of such molecules or in the production of petroleum coke.
Although cracking processes have not been developed specifically for use on asphaltenes, some processes have been developed for use on asphaltene-containing heavy hydrocarbon mixtures. These processes include the Taciuk kiln process (as shown, for example, in U.S. Pat. No. 6,589,417) and non-Taciuk pyrolysis (as shown, for example, in U.S. Pat. No. 5,961,786). Both of these processes involve endothermic reactions that require significant energy. Typically, these processes burn a portion of the hydrocarbons to sustain the reactions. The remainder often is less than 50% of the original material. Moreover, carrying out these processes usually requires the use of furnaces and other expensive capital equipment.
Some references disclose the oxidation of aromatic hydrocarbons, including polycyclic aromatic hydrocarbons, in the context of remediation. These references include U.S. Pat. No. 5,849,201 (the '201 patent) and International Patent Publication No. WO 01/32936 (the '936 publication). The '201 patent discloses the “rapid remediation of aromatic hydrocarbons, and especially polycyclic aromatic hydrocarbons (PAHs), in contaminated materials, such as soils, sludges, tars, sands and liquids using catalysts in conjunction with ozone, oxidants and surfactants.” The '936 publication discloses the remediation of PAHs by chemical oxidation followed by biological treatment. The processes disclosed in these references involve total oxidation of aromatic hydrocarbons into very low molecular weight products, such as carbon dioxide. Since virtually all of the energy contained in the aromatic hydrocarbons is consumed, these processes generally are not suitable for use in upgrading asphaltenes to form useful hydrocarbon products.